The present invention relates to switching mechanisms, such as limit switches for electrically driven actuators, either linear or rotary actuators.
Such actuators are typically utilized whenever either a thrust force or a torsional force needs to be applied. Examples of the utilization of such actuators is in the operation of lever arms, cranks, slides, flap valves, gate valve, globe valve, damper, etc. Such actuators are utilized for alternatively moving or rotating objects between predetermined positions. Exemplary of the type of actuators in which the limit switch of the present application can be utilized are the actuators shown in parent application Ser. No. 100,281 and rotary actuators such as shown in U.S. Pat. No. 4,022,309 (the subject matter of such patent is hereby incorporated by reference). In operating such actuators, limit switches have typically been utilized for either turning off the actuator when it has reached a certain predetermined position or for controlling the operation of associated equipment in dependence upon the position of the actuator. For this purpose, a plurality of switches are included within the switching mechanism which is coupled to the actuator.
It has been common with such limit switches to utilize a single drive gear that is coupled to the actuator through an appropriate set of gears. Each of the switches is coupled to the drive gear through a corresponding one of a plurality of planetary gears that surrounds the drive gear. In order to set the switches, the drive gear has been moved out of engagement with all of the surrounding planetary gears, each of which planetary gears serves to operate one of the switches. When the main drive gear is disengaged, all of the planetary gears are then free to rotate and be set. In order to enable all of the planetary gears and switches to be appropriately set, when the drive gear is disengaged, it is latched into the disengaged position and remains there until removed from such position.
Such a switching mechanism as that described above exhibits several drawbacks which can lead to a malfunctioning of the system. First, since the drive gear is latched into its disengaged position and must be unlatched and removed from such position for the switch mechanism to operate, often during the utilization of the actuator and the limit switch, the operator will fail to remove the drive gear from its disengaged position and hence the limit switch remains inoperative. In addition, since all of the planetary gears are free to rotate when the drive gear is disengaged, it is possible for several of the planetary gears to accidently rotate and thereby be improperly set for actuation at the wrong time.
A plurality of different types of control mechanisms for actuating the switch in dependence upon the position of a set of gears are shown in the prior art. Typically, such mechanisms are part of various timing mechanisms. Illustrative of such control timers are those embodiments shown in U.S. Pat. Nos.: 2,854,855 to Dudley; 2,973,659 to Gallagher et al.; 3,180,168 to Harris; 3,268,677 to Schembera; 3,610,847 to Houpt; and 3,612,789 to Marquis et al.